My GF sometimes says to me things like "you are gay" "you look like gay" and this kind of nags , hope you could help me to handle those things ( of course she doesn't really mean that , but i don't have much to say when she says me that .. it's shutting me up ).

She is joking with you and you know it. You need to not be very sensitive. If she can say shit like that and then sense that you dont give a fuck, thats an easy DHV for you. So just smile and ignore, but dont only pretend you dont care, you should REALLY not care. You can joke back with her an say something like: "no I am not... well there was one time when I...." and then start laughing and cracking yourself up. Just dont take yourself too seriously, be the rock she wants you to be. Treat it as a shit test if you want, though I am not sure it can be treated as such. But maintain your emotional state, and remember that to see yourself through your own eyes and that you dont need peoples' validation .

Thank you ,I've thought that alpha male should not accept this such of behavior from the woman.